A. Field of Invention
This invention introduces techniques to improve the efficacy and color rendering of electric lamps. Our invention utilizes the advantageous properties of: (1) candoluminescent materials, (2) high temperature low thermal capacity insulating materials, (3) discriminative reflective filters, and (4) integration of items 1 through 3 into a cooperative, co-generating arrangement using non-precise energy concentrating shapes for the form of the discriminative reflective filter. A secondary aspect of this patent is an improved efficacy for linear polarized light.
B. Description of Related Art
Some prior art provides a candoluminescent coating for an incandescent filament. Other prior art replaces the metal tungsten incandescent filament with resistive carbon doped candoluminescent material filament that heats to luminescence when an electrical current is applied. The candoluminescent filaments are lower temperature visible light generating sources that generate light via luminescence rather then black body radiation as utilized in the prior art tungsten incandescent filament designs.
Some prior art in the tungsten incandescent filament designs improves efficacy by increasing the temperature of the tungsten incandescent filament. The tungsten filament shifts its output spectrum toward the visible as the temperature is increased in accordance with the physics of blackbody radiation rules. Increasing the tungsten filament temperature is achieved by making the filament thinner. Typical operating temperature of a 75-100 watt tungsten incandescent filament is approximately 2550.degree. C.
Other efficacy improvements utilizing discriminative reflective filters are described in the prior art, and applied in cases where the geometry fits the stringent focusing requirements. These designs provide a reflective discriminative filter, which allows the desirable wavelengths to transmit through the filter. The reflected wasted energy is precisely focused onto the tungsten incandescent filament, which allows energy recycling and light regeneration. Nearly ninety percent of the energy is wasted to IR radiation in the conventional incandescent tungsten filament design; therefore, energy recycling using the discriminative filters offer potentially a great energy saving.
The reflective discriminative filter prior art describes improvements to the design in several areas. These include: (1) filter's transmission efficiency for the desirable wavelengths, (2) filter's reflection efficiency for the undesirable wavelengths, (3) filter temperature survivability and, (4) identification of optically accurate shapes for the reflective filter substrate such as ellipsoidal, spherical, cylindrical or lens shaped in order to accurately focus the reflected energy onto the small area provided by the incandescent filament. Pertinent prior art designs are identified and discussed in the next section.
1. Prior Art and Disadvantages
The Prior art discussion below is grouped into the categories of: candoluminescent electric lamp designs, candoluminescent material selection, low thermal capacity structures and reflective discriminative filter designs.
a) Prior Art for Candoluminescent Electric Lamps
Two patents suggest use of candoluminescent materials as a replacement for the metal tungsten filament.
Use of candoluminescent material as an incandescent light source is suggested as a porous coating material on an incandescent filament. U.S. Pat. No. 4,539,505, by Riseberg; Leslie A. and entitled "Candoluminescent Electric Lamp Source," describes an electric lamp with a filament coated with candoluminescent material. The filament has a resistive core, which is heated electrically. Infrared radiation emitted by the resistive core is converted to visible light by a sheath of candoluminescent material surrounding the resistive core. The filament may be a sintered composition of carbon, ceric oxide and thorium dioxide.
U.S. Pat. No. 4,016,446 by Cadoff; Laurence H. entitled "Refractory-oxide-Based Incandescible Radiators and Method of Making" describes a design to make photo-luminescent semi-conductive element that replaces the tungsten incandescent filament in electric lamps. The filament includes a thin oxide coating, selected to improve the visible radiation emission by luminescence.
There are several design disadvantages of U.S. Pat. No. 4,539,505 and U.S. Pat. No. 4,539,505. (1) The coated incandescent filament design does not improve on usage of reflective filters to regenerate the wasted energy because the target filament remains a small target requiring accurate focusing of the reflected radiation. (2) If the temperature of the filament is too hot, thermal quenching occurs which causes the luminescent material to shift its output luminescence into infrared wavelength versus the desirable visible light. The filament then becomes a blackbody light generation unit, losing all advantages of the potential lower temperature luminescence phenomena. (3) The output spectrum of a luminescent coil is restricted to the wavelengths available from the luminescent material, and does not include the wavelength spectrum of a tungsten incandescent filament using blackbody radiation.
b) Prior Art Identifying Candoluminescent Materials
Several prior arts identify materials other than thorium and calcium oxide for use in gas lanterns. The disadvantage of these prior arts is restricting applicability to gas lanterns.
U.S. Pat. No. 4,532,073 by Cornu; Aime, et. al. entitled "Candoluminescent Material and its Preparation" identifies an alternative for the radioactive thorium oxide. The candoluminescent materials are a mixture formed into a netting of zirconium oxide, calcium oxide, aluminum oxide and/or magnesium oxide. It is prepared by impregnating a combustible textile with a solution of zirconium and calcium salts, optionally containing aluminum, iron, manganese, praseodymium and/or cerium salts and then subjecting the impregnated textile to a combustion process in order to eliminate the textile and transform the salts into oxides.
U.S. Pat. No. 5,124,286 by Edgar; John P. entitled "Incandescent Mantles" provides a mantle composed of zirconia, yttria, erbia and ceria. The mantle for incandescent gas lamps can be made of a substrate impregnated with a solution of oxides of zirconium, erbium, yttrium and cerium. This mantle produces light outputs and color comparable to that of thorium mantles.
c) Prior Art Identifying Low Thermal Capacity Structures
No prior art was identified that describes utilization of existing low thermal capacity insulators as a method to improve efficacy for electric lamps.
d) Prior Art Identifying Discriminative Filter Designs
Selected prior art designs that use discriminative reflective filters to transmit the desirable wavelengths, and reflect the undesirable wavelengths back to the incandescent filament in order to heat the filament and cause energy recycling are identified below.
U.S. Pat. No. 2,859,369 Williams et al. provides a method to selectively reflect back to the incandescent filament the infrared energy. This is accomplished by providing an infrared filter that selectively reflects the wasted infrared light back to the filament, and allows the visible light to transmit through the filter. A small filament is at the geometrical center of a spherical surface which is coated with the reflecting film. The reflecting film precisely reflects the infrared light back to the small incandescent filament, thus recycling the energy into visible light. The inside of the film is coated with a Raleigh scatterer which acts to selectively scatter the desirable visible component of the radiated light out of the lamp.
Follow-on prior art to U.S. Pat. No. 2,859,369 improved aspects of the original patent. Selected pertinent examples of the reflective filter design are identified and discussed below.
U.S. Pat. No. 4,366,407 Walsh, Peter titled "Incandescent Lamp with Selective Color Filter" uses a transparent heat mirror coating on the lamp envelope. The heat mirror transmits desirable radiation in the visible range to produce a desired color and reflects the undesirable radiation back to the filament for energy recycling. U.S. Pat. No. 4,366,407 expands the design to include specific wavelengths in order to output a selected color.
U.S. Pat. No. 4,535,269 Tschetter; Charles D., et. al. titled "Incandescent Lamp" discloses a lamp having an incandescent filament, an improved inner shaped bulb and an infrared reflective film on the outer surface of the inner bulb. The inner bulb has an ellipsoidal shape which in conjunction with the infrared film, focuses the reflected IR back onto the incandescent filament. However, the ellipsoidal shape is an alternate shape still requiring precision optical focusing.
U.S. Pat. No. 4,663,557 Martin, Jr.; Robert L., et. al. titled "Optical Coatings for High Temperature Applications" discloses a coating that can withstand temperature environments in excess of 500.degree. C. A tubular halogen lamp's efficiency is improved by twenty-five percent with the reflecting IR filter design; however, as the filament warps, this efficiency decreases because the filament warps away from the focal point.
The prior art cited above have the following collective disadvantages.
(a) Incandescent Filaments are the Only Recycling Body
All of the patents restrict the energy recycling by focusing the wasted energy back to the originating small tungsten incandescent filament. No secondary light generation sources are considered such as passive candoluminescent mantles. Discriminative reflective filters utilized with incandescent candoluminescent elements are not considered.
(b) Filament Coils Do not Fully Capture Reflected Energy
Successful precise aiming of wasted radiation energy onto the tungsten filament does not fully capture the energy because the coiled tungsten incandescent filament is not a solid body, but a coiled spring that has gaps between the coils. Part of the reflected light that is successfully aimed at the incandescent filament passes through the open parts of the coiled filament without striking the incandescent filament body wire.
(c) Small Filament Target Requires Precision Optical Focusing
A prior art disadvantage is the requirement that the reflecting substrate supporting the discriminative filter conform to an optically precise form sufficiently accurate to focus the wasted energy back to the small incandescent filament. The prior art requires the filament to be at the focal point of a optically accurate substrate. Because of the strict focusing accuracy, the prior art's focusing geometry is limited to spherical, tubular, ellipsoidal or lens shaped envelopes with the tungsten filament at the precise focus. The required precision makes the filter uneconomical and impractical.
The prior art designs further require sufficient structural temperature stability to avoid temperature induced warping which causes the focused energy to miss the filament because of structural and filament warping. The tungsten filament represents such a small target, that relatively high optical filter substrate shape stability and accuracy is required to successfully direct the wasted energy back to the filament. If the focal point misses the filament, the energy is lost to lamp heating, and in may cases lamp base heating. In most cases, filament heating and warping moves the filament out of the focal point. A typical coiled filament in a PAR (parabolic aluminized reflector) lamp increases length by approximately 20% when heated, causing significant filament sag.
The design for the tubular halogen lamp in U.S. Pat. No. 4,588,923 by Hoegler; Leonard E., et. al. provides a simple geometry where the existing exterior lamp envelope acts as a reflecting shape focusing the wasted light back to the tube's center onto the filament. A design disadvantage is that it does not accommodate filament warping. The filament does not remain at the tube's center because of heat induced warping. Thus any heat induced sagging or warping moves the filament from the tube's center apex, causing reflected energy to miss the incandescent filament, and causing a lamp temperature increase. The filament continues to warp with usage causing energy recycling efficiency degradation. Another disadvantage is the filter's temperature survivability requirement that requires the filter material to be at some distance from the incandescent filament to avoid overheating. As the filament warps, parts of the filament approach the discriminative filter, causing local hot spots that damage the discriminative filter. If the filter is mounted on the exterior, any contamination from handling or dust settling on the lamp also causes local heating which damages the filter, and adds to further heating and filter damage.
(d) Design Tradeoff Between Self Supporting and Efficiency
The tungsten incandescent lamp requires the incandescent filament to be both a self supporting structure and the source of desirable light. Efficiency is gained by heating the incandescent filament to higher temperatures usually achieved with smaller diameter incandescent filaments, but the self supporting requirement requires thicker wire for survivability. There is therefore a tradeoff between efficiency and the self supporting requirements which determine life-span and shock resistance. Any supporting structure acts to cool the incandescent filament, requiring more energy input to compensate for supporting structure's thermal drain.
(e) Restricted to Incandescent Lamps
The prior art restricts their applicability to incandescent lamps, and does not include fluorescent lamps. No patents include use of the discriminative polarized reflective filters to improve efficiency for fluorescent lamps.
(f) Full Spherical Light Generation
Common incandescent filament designs emit light in a full spherical radiation pattern which includes emitting light energy in undesirable directions such as toward the lamp base. The full spherical emission is mitigated partially by use of a reflector which takes the form of a mirror plating inside a cone shaped lamp envelope, or as an external reflector. The reflectors form a forward projected beam shape, but undesirably act to reflect some energy toward the lamp base. Other methods to minimize the light projected at the lamp base require mounting the cylindrical filament so that one end of the cylindrical element points at the lamp base which reduces the filament's radiant area directed toward the lamp base.
(g) Focusing Causes Filament Weak Spot
The spherical precision focusing configurations that concentrate the discriminative filter reflected energy onto one place on the filament causes excessive heating at that point, which forms a weak spot and causes filament failure.
(h) Polarized Reflective Filters not Mentioned
The prior art does not mention any method of improving efficacy for generation of linear polarized light by reflecting and recycling the wasted radiation by use of commercially available reflective polarizing filters. The patents restrict their applicability to wavelength bands.